Arc welding method and apparatus

ABSTRACT

A process and apparatus for welding a metal component to a metal workpiece. The component typically comprises a metal weld region and a threaded connector region and the apparatus includes a weld head comprising a nozzle for holding the weld region of the component adjacent the workpiece. The weld head induces a weld arc between the weld region of the component and the workpiece to create a weld pool of molten material. The weld head subsequently moves the weld region into the weld pool to permanently join the component to the workpiece. The apparatus further comprises a pressurized fluid source and a fluid flow control means for directing the pressurized fluid between the weld head and the component an weld pool so as to deflect any airborne fluid residue of the weld pool away from the connector region of the component.

The invention relates to a process and apparatus for arc welding of ametallic component to a metallic structure. More particularly, theinvention relates to the welding of a metallic stud or nut to a metallicsheet on which stud or nut is to be used as an anchorage.

The welding of metallic studs and nuts to a metallic structure by meansof arc welding is a widespread process found in particular applicationin the automotive industry. The exact method of the welding process canbe relatively varied but the general principal involves the formation ofan electric arc between the stud and the metal sheet effecting relativemelt of the metallic materials in the region of the arc so that themetal component can then be lowered into the melt which is formed in thefusion region to result in a strong welded connection being formedbetween the component and the metal structure on subsequent cooling.

One form of welding process is the so called drawn arc welding processwhich involves positioning the component to be welded to the metal sheetwithin a weld gun and bringing the component into electrical contactwith the metallic surface to complete an initial circuit indicating thatthe metal component is in contact with the metal sheet. The weld cycleis then initiated whereby the stud is withdrawn from the work surfaceinducing a pilot arc which serves to help clean both the component andthe work surface before a main welding current is initiated creating aweld arc between the raised component and the metal sheet. The weld arcserves to form a pool of molten metal on the sheet material and also onthe metallic component. The welding apparatus then causes the componentto be plunged into the molten metal whereby as the weld pool solidifiesit forms a homogenous joint. The entire process takes less than a secondand forms a joint which in fact is stronger than material that hasactually been welded. Such a drawn arc welding process is standardwithin the welding industry and is used to attach both studs and nuts tometal sheets which allow further fastenings to be connected thereto. Inthis manner studs themselves may often be threaded to receive aco-operating threaded nut or a nut itself may be welded directly ontothe sheet in order to receive a screw threaded connector. Usually suchstuds and nuts are to enable earthing connections to be made to thesheet metal and thus require good electric contact to be made betweenthe stud or nut and the appropriate connector element fixed thereto.However, it has been found that even with the cleaning function of thepilot arc, the intense heat generated by the arc during the weldingprocess results in the formation of vaporised carbon and otherimpurities which can result in a “smoke” emanating from the moltenmaterial. Condensation of this smoke and vaporised impurity on thethreads above the welded nut or stud can serve to inhibit electricalcontact with the subsequent connection and impair the threadedengagement between the component and threaded connector.

Furthermore, it has been found that due to the reactive forces generatedby the formation of the arc itself and also by the driving of thecomponent into the molten metal can result in the formation of splashesof molten metal whereby if such splashes land on the thread of the nutor the stud, then they again will solidify to inhibit the screw threadedoperation of such nut or stud. It is therefore an object of the presentinvention to provide for an improved welding process and weldingapparatus to alleviate the aforementioned problems in a manner whichwill not inhibit the speed or quality of the welding procedure.

According to one aspect of the present invention there is provided amethod of welding a substantially metal component to a metal workpiece,comprising the steps of: creating a weld arc between said component andmetal workpiece to create a weld pool of molten material and initiatinga pressurised fluid flow over said component and the weld pool todeflect any airborne fluid residue of the weld pool away from saidcomponent during the displacement of the component into the weld pool.

Preferably, where the method is applicable to a component whichcomprises a metal weld region and a connector region, the weld arc iscreated between the metal weld region of the component and the metalworkpiece to create a weld pool and the pressurised fluid flow isinitiated so as to be disposed between the connector region of thecomponent and the weld pool to deflect the fluid residue of the weldpool from the connector region. Usually the flow of pressurised fluid isinitiated as least substantially simultaneously with the creation of theweld arc or before creation of the weld arc.

Where the connector region is threaded, the method will usually comprisethe step of deflecting the fluid flow through a channel formed by thethread of the threaded region. In particular, where the component is aweld nut the pressurised fluid flow is directed through the centralaperture of the nut to create a positive pressure within the aperture ofthe nut which prevent any splashes of molten weld material or gases fromentering this region. The method will also preferably comprise the stepof placing a solid cylindrical insert in frictional engagement with theinternal threads of the nut in order to form sealed channels with thethread through which the fluid flow can then be directed. In this mannerthe pressurised fluid is further compressed through this threadedchannel to create a high positive pressure which prevents any airborneparticulate from the weld procedure from being thrown or drawn into thethreaded region of the nut.

The pressurised fluid may be given a straight flow path prior to beingdirected through the nut. This flow path can be induced by passing thefluid through at least one longitudinally extending channel, usuallyformed within a solid control valve placed in the fluid path, and moreusually the flow is induced by passing through six such channels, whichare equally spaced angularly about the central axis of the fluid flowpath.

The pressurised fluid may also be given a spiral flow path prior tobeing directed through the nut. Thus when the fluid flow engages withthe spiral threads of the nut it has already partially aligned with suchthreads and therefore readily engages and enters the channels formedbetween the threads of the nut. This spiral flow path is preferablyinduced by passing the fluid through at least one spiral channel,usually formed within a solid control valve placed in the fluid path,and more usually the spiral flow is induced by passing through six suchchannels, which are equally spaced angularly about the central axis ofthe fluid flow path. The spiral channels are usually set to deflect thefluid flow at an angle of between 10 and 80° relative to a planeperpendicular to the direction of fluid flow and more particularly theangle of deflection generated is between 50 and 70°.

The pressurized fluid may also b allowed to expand after the spiral flowpath is induced therein. Preferably, the fluid use in this method willbe compressed air directed from a pressurized air source at a flow ateof between 5 and 30 liters per minute and preferably between 10 and 20liters per minute.

Furthermore, according to a second aspect of the present invention thereis provided apparatus for directing a pressurised fluid flow over asubstantially metal component during arc welding, the fluid flow beingdirected by said apparatus so as to deflect any airborne fluid residuecreated by the welding process away from the component.

According to a further aspect of the present invention there is alsoprovided welding apparatus for welding a substantially metal componentto a metal workpiece, said component comprising a metal weld region anda connector region, said apparatus comprising a weld head having meansfor holding said weld region of said component adjacent said workpieceand inducing a weld arc between said weld region and workpiece to createa weld pool of molten material, whereby the weld head subsequentlydisplaces said weld region into said weld pool; said apparatus furthercomprising a pressurised fluid source and a fluid flow control means fordirecting said pressurised fluid over said component and the weld poolso as to deflect any airborne fluid residue of the weld pool away fromsaid connector region of said component.

Usually such apparatus will comprise control means for initiating fluidflow at least substantially simultaneously with or before the creationof the weld arc. Such control means will usually be by means of acomputerised control station as are conventional for arc weldingapparatus (both automated and hand held) whereby such control unit willdetect, by means of a test voltage, when welding should occur andthereby automatically directs a weld current to the weld head to createthe weld arc. Such a computerised control unit can, simultaneously orslightly prior to inducing the weld current, initiate fluid flow fromthe fluid source in a conventional manner such as opening a valve or anyother conventional method of transmitting a pressurised fluid from apressurised fluid source. This computerised control unit will alsocontrol displacement of the weld head and nozzle.

The welding apparatus will usually be used with a component having athreaded connector region whereby the fluid control means will comprisea directing member on the outer edges of the threads so as to form asubstantially sealed channel therewith and to then direct such fluidflow through this thread channel. With an externally threaded membersuch as a screw threaded stud such a directing member may form a tubularbody which slides over the exterior surface of the stud so as to engagesuch threads, but in the case of a threaded nut then the outer edges ofthe threads are directed about the internal periphery of the internalnut aperture in which case a cylindrical body is inserted into the nutso as to engage these threads.

The fluid flow control means will usually comprise a substantiallyhollow fluid transmitting member with an end stop for substantiallyforming a sealed engagement with the upper surface of a weld nut so thatfluid flow is directed through the central aperture of such nut. Suchfluid flow will then be prevented from continued displacement throughsuch nut where the cylindrical body has been inserted and thus is forcedinto the channel formed between the thread of the nut and thecylindrical body to pass therethrough. This provides the advantage ofspecifically directing the pressurised fluid flow through the threads ofthe nut and also serves to increase the pressure of the fluid throughthese channels thereby preventing any airborne residual particles fromthe weld pool from entering by the nut thread.

The welding apparatus will also preferably comprise a control valvedisposed between the fluid source and the nut for inducing a flow pathin the fluid flow. This control valve will usually comprise a solid bodyhaving at least one channel extending therethrough. The control valvewill be cylindrical and may have six channels formed about its peripheryso as to be equally spaced angularly about the axis of such valve. Thechannels may by spiral and, if so, will usually be formed at an angle ofbetween 10 and 80° to a plane perpendicular to the direction of flow.

In addition, a deflector may be disposed in the fluid flow in front ofthe control valve and angularly inclined in the direction of fluid flowto gradually deflect fluid flow towards the entrances to the spiralchannels. This is to alleviate the formation of eddy currents wherebythe pressurised fluid is forced through the smaller apertures of thespiral channels which could disrupt formation of the spiral fluid flow.Usually such a deflecting member comprises a cone.

In addition, where the fluid flow has been compressed through channelsin a fluid control valve the fluid control means may comprise anexpansion chamber in which the fluid may enter after passing through thefluid control valve to allow expansion of the pressurised fluid afterspiral flow is induced. This expansion of the pressurised fluid enablesthe spiral flow path to be retained but reduces the pressure slightlyafter having been compressed through the channels in the control valveso that it more readily engages with and enters into the channels formedbetween the threaded region of the nut and the cylinder placed therein.

This welding apparatus is highly applicable to existing weldingapparatus whereby the leading arm of conventional weld heads can beutilised to form a substantially airtight cylinder through which thefluid flow may pass and thus be directed to the component during theweld operation whereby the weld control valve can be simply incorporatedwithin the end of such a member 14.

The invention will now be described, by way of example only, withreference to the accompanying illustrative drawings as follows:

FIG. 1 is a cross sectional view of a conventional nozzle of anautomatic weld head used in drawn arc welding of nuts (Prior Art).

FIG. 2 is a cross sectional view of a nozzle of an automated weld headof the present invention with a loaded component;

FIG. 3 is a plan view from above of the fluid control valve of thenozzle of FIG. 2;

FIG. 4 is the nozzle of FIG. 2 showing operative connection of a weldnut to a metal sheet;

FIG. 5 shows a second embodiment of a nozzle of a weld head of thepresent invention; and

FIG. 6 shows another embodiment of the pin having co-axial grooves.

Referring first to FIG. 1, there is shown a nozzle arrangement (8) of aconventional automatic weld head used in drawn arc welding. In the viewshown in FIG. 1, the inner loading arm (14) is shown in a loadedposition (relative to a sleeve (10)) although no component is shown.This is for convenience of description of the prior art.

The nozzle (8) comprises a hollow elongate cylindrical sleeve member(10) made of an electrically conductive material such as copper orbrass. The sleeve further comprises elongate slots (not shown) extendingupwardly from an open outermost end (12), which slots serve to allowradial expansion of the remote end of the sleeve if an internal radialforce is applied. Due to the resilient nature of the sleeve, these slotsserve to allow the passage of an object having a larger diameter thanthat of the unstressed sleeve if sufficient force is applied to thatobject. This will be described in more detail later.

The sleeve member (10) is mounted in electrical contact with acomputerised weld control unit (not shown) as is conventional within theart. The weld control unit provides for controlling and application ofthe appropriate weld current.

The automatic weld head further comprises a loading arm (14) ofsubstantially insulating material which is displaceable co-axial throughthe sleeve member (10) (vertically as viewed in FIG. 1 and FIG. 3). Theloading arm is displaceable by conventional servo or electromechanicalmeans which are again conventional within the art and need not bedescribed in more detail. Operation of the drive mechanisms are againcomputer controlled—albeit that such computer control may be in responseto an operation input, such as activation of a switch.

The loading arm (14) is substantially hollow and has mounted on its freeend a cylindrical stop nut (15) mounted co-axial therewith. This nut(15) has mounted co-axial therein a ceramic or metal pin (18).

The pin (18) has a head (20) having a diameter substantially greaterthan that of the body (17) of the pin (18) whereby the head (20)projects externally of the loading arm (14).

The loading arm (14) further comprises an end stop member (22) againmounted co-axial therewith which presents a radially extending end faces(24) for engagement with an appropriate component.

Referring now to FIG. 2, the nozzle of the present invention is shownand corresponds substantially to the prior art with two exceptions to bedescribed. Firstly, the design of the nozzle (8) again comprises ahollow elongate cylindrical sleeve member (10) housing a loading arm(14) similar to that described with reference to FIG. 1. Furthermore,the nozzle (8) shown in FIG. 2 is loaded with a component, in this casea rotary weld nut (28), which has been displaced axially through theouter sleeve (10). Basic loading and operation of the nozzle with thisnut (28) will be described later.

The two major differences between the current invention and that of theprior art reside in the replacement of the stop nut (15) of the priorart with a cylindrical fluid control valve (16) again having co-axiallymounted therein a pin member (18) wherein the pin (18) also enjoys inmodification whereby its inwardly directed end (21) forms a truncatedcone as it extends away from the free end (12) of the nozzle (8). Theengagement between the valve (16) and the end stop member (22) and thearm (14) forms a substantially airtight fit and whereby engagement ofthe pin (18) within the valve (16) also forms a substantially airtightfit.

For clarity, whilst the nozzle (8) in FIG. 2 is shown in cross section,the valve (16) is shown in profile in order that its externalconfiguration may be clearly seen.

The fluid control valve (16) comprises in its radial outer surface aseries of six grooves (26) (which are shown in FIGS. 2 and 3) equallydisposed angularly about the circumference (at 60° relative to eachother) and which spiral about this outer surface at an angle (δ) ofapproximately 60° relative to a plane extending perpendicular to theaxis (A) of such valve. These spiralling grooves (26) serve to providefor fluid communication between the hollow central chamber (29) of theloading arm (14) and the exterior thereof. The pin (18) serves to form arelative seal with the interior surface (31) of the cylindrical valve(16).

The loading arm (14) has connected thereto a pressurised fluid source(not shown) which is again controlled by the weld control unit, allowingfluid to be introduced into the loading arm (14) under pressure to beexpelled through the fluid control valve along the appropriatespiralling grooves (26).

In operation the automatic weld head is mechanically displaceable bymeans of motor driven or hydraulically driven means into an engagementwith a workpiece such as sheet metal. The weld head itself, in a restconfiguration, will hold the loading arm (14) axially removed from thesleeve member (10). In operation a weld nut (28) is fed by means of anautomated feeder to an entrance port (not shown) of the nozzle, at whichstage the loading arm (14) is displaced so as to engage with the nut(28) whereby the pin head (20) is received within the central threadedaperture of the nut (28) in a substantially friction fit with theinwardly directed threads of such nut and to pass partially through saidcentral aperture to project externally of said nut as the end faces (24)of the end stop (22) engage with an upper surface of said nut (see FIG.2). Continued displacement of the loading arm into the sleeve member(10) effectively forces the nut (28) through said sleeve member (10).

The nut (28), as best seen in FIG. 2, varies slightly from aconventional nut in that it has on its lower face (39) a peripheralridge (36). To improve weld performance this ridge may taper to anannular apex, having a “V” shaped configuration. The pin (18) projectsexternally of the threaded portion of the nut (28) so as to be partiallyreceived within a chamber (41) formed by this ridge (36).

Furthermore, the nut (28) will have a diameter slightly greater than theinternal diameter of the sleeve member (10) to provide for frictionalengagement between the nut and the sleeve. This serves to retain the nutfrom simply “falling” through the sleeve (10) as it is pushed through bythe loading arm (14). This frictional fit further serves to restrain thenut (28) as the pin of the loading arm (14) is driven therethrough. Asdiscussed above, the sleeve (10) has an array of longitudinallyextending slits which permit for expansion of the sleeve (10) as the nutis forced therethrough. This allows for controlled displacement of thenut along the sleeve member (10) under force applied by the loading arm(14).

In operation, the nut is displaced through the sleeve (10) at apredetermined distance so that the outer ridge (36) of the nut projectsexternally from the sleeve (10) a predetermined distance (D) as best seein FIG. 2.

The automated weld head then serves to displace the nozzle (8) towards ametallic work surface (40). The work surface will usually comprisemetallic sheet material, for example as used in the bodywork of anautomobile. The work surface is maintained in electrical contact withthe weld control unit, as is the weld nut (28) by virtue of electricalcontact between the sleeve (10) and the weld nut (28). A low voltage isapplied by the weld control unit which is able therefore to determinecontact between the nut (28) and the work surface (40) since contacteffects completion of the appropriate electrical circuit generated bythe weld control unit. In this position the weld control unit, as isconventional, determines the exact relative position between theautomatic weld head, weld nut and work surface and initialises aconventional weld cycle whereby the automatic weld head withdraws theweld nut away from the work surface and applies a weld current to thesleeve and nut (28) which induces a weld arc to form between the nut andthe work surface creating a pool of molten metal to form on the ridge(36) of the weld nut and the work surface (40). Immediately followingwhich, the weld head serves to plunge the nut (28) into the molten metalof the weld pool. As the weld pool solidifies it forms a homogenousjoint between the nut and the metallic work surface which is usuallystronger than the metallic components of the nut or work surface. Theweld head then withdraws the sleeve (10) and loading arm (14) out ofengagement with the nut (28), whereby the frictional engagement forcesbetween the sleeve and the nut and the pin (18) and the nut (28) areovercome by the rigid engagement of the nut with the work surface. Asseen in FIG. 4, the weld pool forms weld joints (43) around the innerand outer periphery of the ridge (36) of the nut (28).

In the welding operation described above, it has been found that thisprocedure can result in significant splashing of the molten metal due tothe intense and rapid melting of the metal and as the nut is driven intoengagement therewith. The droplets of molten metal formed by suchsplashes can land on the internal threads of the nut (28). In addition,due to impurities both in and on the surface of the nut and the worksurface, notably carbon, the high temperatures generated by this type ofwelding procedure can result in the generation of vaporised impuritiesand burnt particles in the form of a smoke. These vaporised impuritiesand smoke may then condense and be deposited on the internal threads ofthe nut (28). Since the nut is intended to receive a fastening element,which may take the form of a screw or bolt, and may be intended to forman electrical engagement between the nut and any screw threaded fastenerfixed thereto, then any impurities formed on the internal thread of thenut could adversely effect electrical contact whereas any moltenmaterial as splashed on the threads of the nut could prevent or makescrew threaded engagement with a screw threaded fastener difficult. Thusthe effects of both these forms of airborne fluid residue from the weldpool are detrimental to the efficiency of the welding process.

This problem has previously been partially addressed by the use of thepin (18) projecting through the central screw threaded portion of thenut to try and prevent splashes from engagement with the screw thread.However, such a feature is only partially successful since the pin head(20) is only capable of engagement with the innermost edges of the screwthreads and thus an open channel is able to extend spirally about thepin head by means of the screw thread. This allows any vapourisedimpurities or smoke to pass over the internal screw threads and alsoallows any splashes to extend at least partially into the screw threadedregion of the weld nut (28).

Therefore, the improved process of the current invention involves anadditional process step during the actual arc welding presses. Referringto the improved weld nozzle of FIGS. 2 and 4, as the weld head lifts thenozzle arrangement (8) away from the work surface so as to create theweld arc, the weld control unit activates the pressurized fluid controlmechanism (usually a valve or other standard fluid control unit) tointroduce pressurized fluid, most usually pressurized air at a flow rateof approximately 10-20 liters per minute, into the hollow central area(29) of the loading arm (14) to thereby pass through the air controlvalve (16) by means of the spiral grooves (26) into a region (50) (orexpansion chamber) between the pin head (20) and the fluid control valve(16) (and sealed by engagement between the nut (28) and stop member(22)) whereby such pressurized air is then forced through the screwthreads of the nut about the in head (20) which creates a positivepressure preventing smoke or vaporized impurities or metallic splashesfrom entering the screw threaded area of the nut (28).

Furthermore, as seen from FIGS. 2 and 4, the innermost end (21) of thepin (18) comprises a truncated cone. Formation of this truncated coneserves to deflect the fluid flow inside the loading arm (14) towards theperipheral entrances to the formed spirals (26) of the fluid controlvalve (16). Reflection of the fluid flow by use of such a conicalsurface helps alleviate formation of eddy currents that could impairfluid flow into the spirals of the valve (16). Furthermore, in oneembodiment of the invention shown in FIGS. 2 and 4, the fluid flow isallowed to expand once it has passed through the spiral grooves (26) ofthe fluid control valve (16) in the region (50) between the valve andthe head of the pin (18). It has been found that by allowing thepressurized fluid or compressed air to expand in this region it helps toimprove the vortex effect created by the spiralled grooves which vortexeffect again assists in displacing the pressurized fluid or air toengage the spiral channel formed between the screw thread of the nut(28) and the pin head (20). It also serves to return the flow rate ofthe compressed air to the desired range of 10-20 liters per minute afterthe additional compression through the fluid control valve (16). Air atthis flow rate is more readily received through the thread of the nut.

The angle (δ) of the spiral grooves formed in the control valve (16) areset at approximately 60°. However it will be appreciated that this angle(δ) may be varied from 10° right through to 90° (i.e. co-axial), asillustrated in FIG. 6, whilst still falling within the scope of thepresent invention. In fact, experimentation has indicated that co-axialgrooves (26″) on an alternative embodiment of the pin (18″) may work aswell or better than spiral grooves in preventing smoke or vaporisedimpurities or metallic splashes from entering the screw threaded area ofthe nut.

The use of spirals within the fluid control valve (16) are utilisedprimarily to create a vortex effect as the pressurised airflow engageswith the spiral threads of the nut (28) to allow for effective fluidflow from the valve and through this threaded region of the nut.However, if the angle (δ) increased to 90° then fluid under pressurewill still be forced through the valve (16) into engagement with thethreads of the nut (28) albeit efficiency may be slightly reduced. Itwill also be appreciated whilst the valve (16), as shown in FIGS. 2 and3, utilise a series of grooves formed about the periphery of the valve(16) such grooves may equally be formed along the inner peripheral wall(31) of this cylindrical valve (16) or alternatively may simply beformed through the solid part of such valve. The critical criterion inthis case is to provide for fluid communication between the interior ofthe arm (14) and the internal threaded region of the nut (28). The valve(16), in its simplest embodiment, may be removed completely.

FIG. 5 illustrates an alternative embodiment to the current invention.In this embodiment, the fluid control valve (16′) is increased in sizeso as to replace the combined valve (16) and pin arrangement (18) ofFIG. 2 so that the valve (16′) projects externally of the arm (14) so asto pass through and frictionally engage with the internal thread of thenut (28′). In this embodiment the spiral grooves (26′) engage directlywith the internal threads of the nut to again pass pressurised fluid(compressed air) into the threaded region of said nut to create apositive pressure preventing transmission of vaporised gas and particlesor molten metal splashes into the internal thread of the nut. Hereagain, the efficiency of the valve in the process can be varied byvarying the angle of the grooves (26′).

It will be appreciated that for utilisation of this invention withregard to a weld nut applied to a sheet metal surface as herein beforedescribed, then an aperture (100) is required to be formed through thatsheet metal material to allow communication between the chamber (41) anda region having a lower pressure than the pressurised fluid introducedinto the arm (14) to effect appropriate pressurised fluid flow. However,it will also be appreciated that the present invention is not limited toa welding process and apparatus for use solely with weld nuts but mayalso be extended to the welding of other components to a metallicsurface. For example, the invention also has benefits within the fieldof stud welding. Stud welding involves a substantially identical processto that described for the welding of nuts to metallic surface butinstead of nuts, the components are studs which comprise a substantiallycylindrical threaded body having an enlarged head, usually circular andco-axial with the stud body. In this situation the head itself is weldeddirectly to the metal in a manner identical to that previously describedfor the nut. When welded to a sheet metal such a stud is intended toreceive a nut or other threaded fastener to provide a similar functionto the nut previously described. Again the formation of molten metal onthis threaded region due to splashing or the formation of impurity oncarbon deposits by the formation of smoke and vaporised impurities willagain be detrimental to this welding operation. Therefore, thisinvention is equally applicable to such stud welding by the introductionof a pressurised fluid flow over the threaded portion of the stud so asto force any gases produced by the welding process or molten metaldroplets formed by splashing during the welding process (airborne fluidresidue) to be forced away from the threaded region by virtue of suchcontrolled pressurised fluid flow. Again compressed air is the mostlikely source of pressurised fluid. Here the fluid flow is used to forma “barrier” between the threaded region and the weld pool.

In its simplest form the invention could be embodied by the position ofa simple tubular delivery valve positioned above the threaded region ofa stud so as to direct air vertically downwards along the threadedregion of the stud whereby it will engage the rear portion of the headof the stud and be deflected outwards thus providing the appropriatefluid barrier preventing splashes or smoke from travelling towards thethreaded region. Alternatively, a series of fine nozzles could bedisplaced around the weld head to again direct pressurised air jets ontothe back of the head of the stud (i.e. the surface of the stud headwhich is not brought into weld engagement with the weld pool) at such anangle that the pressurised gas is then deflected so as to pass over thesurface of the stud head and displaced radially outwardly from thecentral portion to again effectively form a pressurised fluid barrierbetween the threaded region and the weld pool whilst meeting theobjectives of this invention. In this manner the compressed air is notdirected onto the weld joints themselves but merely flows radially awayfrom the threaded central portion of the stud so as to deflect any smokeor molten droplets away from this threaded portion but without directlyor adversely affecting the melt pool and weld joints about the peripheryof the head of the stud. Obviously more complicated apparatus andmethods may be employed to effect the same end result for stud welding.

It will also be appreciated for stud welding that the threaded portionitself need not be metallic but may be of plastics or other materialprovided that electrical contact can be achieved with a metal head ofsuch a stud.

Furthermore, the fluid flow itself may comprise preheated air (orliquid) to prevent any undue enforced cooling of the melt pool duringthe weld process.

Whilst the specific embodiment of both the process and apparatus hasbeen directed to use with an automated weld head system, it is equallyapplicable to a hand held welding gun which operates in a similar mannerutilising a computerised weld control unit to control the actual weldingoperation but in this situation conventional a hand held weld gun wouldsimply require an additional control unit to introduce the pressurisedfluid upon operation of the trigger to effect manual welding. A handheld weld gun would require the operator to position the weld nut orweld stud in engagement with a metallic surface (40) and then toactivate the weld gun by depressing a trigger. The weld gun will thencomprise left means to withdraw the nozzle and nut from the metallicsurface a sufficient distance to create the weld arc. Such a situationoperation of the trigger switch of the gun would also introduce theappropriate flow of pressurised gas in the manner discussed withreference to the automated system above.

What is claimed is:
 1. A method of welding a substantially metalcomponent to a metal workpiece, comprising the steps of: engaging thecomponent with a welding machine; circumferentially sealing a fluid flowregion by direct engagement between a seal and only a predeterminedportion of said component; creating a weld arc between said componentand metal workpiece to create a weld pool of molten material; andinitiating a pressurized fluid flow between the welding machine and thefluid flow region to deflect any airborne fluid residue of the weld poolaway from said predetermined portion during the displacement of thecomponent into the weld pool.
 2. The method as claimed in claim 1 inwhich said component comprises a metal weld region and a connectorregion, said connector region forming the predetermined portion,comprising the steps of: creating the weld arc between said metal weldregion of said component and metal workpiece to create the weld pool ofmolten material; and initiating the pressurized fluid flow so as to bedisposed between the connector region of the component an the weld poolto deflect any airborne fluid residue of the weld pool away from saidconnector region of said component.
 3. The method as claimed in claim 2,further comprising initiating the flow of pressurized fluid at leastsubstantially simultaneously as the creation of the weld arc.
 4. Themethod as claimed in claim 2, further comprising initiating the flow ofpressurised fluid before the weld arc is created.
 5. The method asclaimed in claim 2, further comprising forming a threaded connectorregion.
 6. The method as claimed in claim 5, further comprising the stepof deflecting the pressurised fluid flow through the fluid flow regionformed by a plurality of threads of the threaded connector region. 7.The method as claimed in claim 2 in which the component is a weld nut,comprising the step of directing said pressurised fluid flow through acentral aperture of said nut.
 8. The method as claimed in 1, comprisinginducing a spiral flow path in the pressurized fluid flow.
 9. The methodas claimed in claim 8, comprising inducing the spiral flow path bypassing said fluid through at least one spiral channel.
 10. The methodas claimed in claim 8, further comprising the step of causing thepressurized fluid to expand after the spiral flow path is induced in thefluid flow.
 11. The method as claimed in claim 8, comprising passing thefluid flow through six spiral channels equally spaced angularly about acentral axis.
 12. The method as claimed in claim 9, comprising settingthe at least one spiral channel to deflect the fluid flow at an angle ofbetween 10° and 80° to a plan perpendicular to the direction of thefluid flow.
 13. The method as claimed in claim 12, comprising settingthe angle between 50° and 70°.
 14. The method as claimed in claim 1, inwhich the pressurised fluid is compressed air further comprisingdirecting the compressed air at a flow rate of between 5 and 30 litersper minute.
 15. The method as claimed in claim 14, comprising directingthe compressed air at a flow rate of between 10 and 20 liters perminute.
 16. A welding apparatus for welding a substantially metalcomponent to a metal workpiece, said component comprising a metal weldregion and a connector region, said apparatus comprising: a weld headoperably holding said weld region of said component adjacent saidworkpiece and inducing a weld arc between said weld region and workpieceto create a weld pool of molten material, whereby the weld headsubsequently displaces said weld region into said weld pool; apressurized fluid source; a fluid seal positionable adjacent only theconnector region of said component; and a fluid flow controller operablydirecting a fluid of the pressurized fluid source between said weld headand said connector region within the fluid seal and the weld pool so asto deflect any airborne fluid residue of the weld pool away from saidconnector region of said component.
 17. The welding apparatus as claimedin claim 16, further comprising a second controller operably initiatingfluid flow one of at least substantially simultaneously with and beforethe creation of the weld arc.
 18. The welding apparatus as claimed inclaim 16, for use with a component having a threaded connector region,in which said fluid flow controller comprises a directing member forengaging with a plurality of outer edges of said threaded connectorregion so as to form a substantially sealed thread channel therewith andto direct said fluid flow through said thread channel.
 19. The weldingapparatus as claimed in claim 18, for welding a weld nut, wherein saidfluid flow controller comprises a substantially hollow fluidtransmitting member with an end stop for substantially sealed engagementwith an upper surface of said nut so as to direct said fluid flowthrough a central aperture of said nut.
 20. The welding apparatus asclaimed in claim 19, in which the directing member comprises acylindrical body to be received within the central aperture of said nut.21. The welding apparatus as claimed in claim 19, in which said fluidflow controller comprises a control valve disposed between said fluidsource and said nut for inducing a spiral flow path in said fluid flow.22. The welding apparatus as claimed in claim 20, in which said controlvalve comprises a solid body having at least one spiral channelextending therethrough.
 23. The welding apparatus as claimed in claim21, wherein the control valve is cylindrical having six spiral channelsformed about its periphery so as to be spaced angularly equidistantthereabouts.
 24. The welding apparatus as claimed in claim 22 which theat least one spiral channel is formed at an angle of between 10° and 80°to a plane perpendicular to a direction of fluid flow.
 25. The weldingapparatus as claimed in claim 21 in which said fluid flow controllercomprises an expansion chamber into which the fluid enters after passingthrough said control valve, causing expansion of said pressurized fluidafter spiral flow path is induced therein.
 26. The welding apparatus asclaimed in claim 25, in which said expansion chamber is formed betweenthe control valve and said cylindrical body.
 27. A method of welding asubstantially metal component being a weld nut having a metal weldregion and a connector region to a metal workpiece, comprising the stepsof: engaging the nut with a welding machine; creating a weld arc betweenthe metal weld region of the nut and metal workpiece to create a weldpool of molten material; initiating a pressurized fluid flow between thewelding machine and the nut so as to be disposed between the connectorregion of the nut and the weld pool to deflect any airborne fluidresidue of the weld pool away from the connector region of the nutduring the displacement of the nut into the weld pool; directing thepressurized fluid flow through a central aperture of the nut; and;placing an insert in frictional engagement with internal threads of thenut to form a sealed channel with the threads through which the fluidflow is directed.
 28. A welding system, comprising: a substantiallymetal weld nut having a metal weld region and a threaded connectorregion formed about a central aperture, the weld adapted for weldattachment to a metal workpiece; a weld head having a sleeve operable tohold the weld region adjacent to the workpiece and induce a weld arcbetween the weld region and the workpiece to create a weld pool ofmolten material, wherein the weld head subsequently displaces the weldregion into the weld pool; a pressurized fluid source; a fluid flowcontroller operable to direct a fluid from the pressurized fluid sourcebetween the weld head and the weld nut and the weld pool so as todeflect any airborne fluid residue of the weld pool away from theconnector region of the weld nut; a plurality of threads of the threadedconnector region; and a directing member including a cylindrical bodyengageable with the plurality of threads of the threaded connectorregion to form a substantially sealed thread channel and operable todirect the fluid through the thread channel.
 29. A welding apparatus,comprising: a substantially metal weld nut having a metal weld region, athreaded connector region formed about a central aperture and an uppersurface, the weld nut adapted for weld attachment to a metal workpiece;a weld head having a sleeve operable to hold the weld region adjacent tothe workpiece and induce a weld arc between the weld region and theworkpiece to create a weld pool of molten material, wherein the weldhead subsequently displaces the weld region into the weld pool; apressurized fluid source operable to supply a fluid; a fluid flowcontroller operable to direct the fluid between the weld head and theweld nut and the weld pool so as to deflect any airborne fluid residueof the weld pool away from the threaded connector region adjacent acentral aperture of the weld nut, the fluid flow controller including: asubstantially hollow fluid transmitting member having an end stop forsubstantially sealed engagement with the upper surface of the weld nut,the transmitting member operable to direct the fluid through the centralaperture of the weld nut; a cylindrical directing member engageable withthe threaded connector region to form a substantially sealed threadchannel and operable to direct the fluid through the thread channel; acontrol valve disposable between the fluid source and the weld nut forinducing a spiral flow path of the fluid; and a deflector memberdisposed in the flow path of the fluid in front of the control valve andangularly inclined in a direction of the flow path, the deflector memberassisting to gradually deflect the fluid toward the thread channel. 30.The welding apparatus of claim 29, wherein the deflector membercomprises a cone.
 31. An arc welding apparatus, comprising: a pluralityof threaded weld connectors each having a plurality of threads; awelding machine having a weld head capable of externally grasping thethreaded weld connector; a sealing element longitudinally displaceablein the weld head, the sealing element operable to contact the pluralityof threads of the threaded weld connector such that a sealed channel isformed between the threads and the sealing element; and a pressurizedfluid source connectable to the welding machine operable to supply afluid flow within the sealed channel; wherein during an operation when aweld arc is generated by the weld machine between the threaded weldconnector and a metal workpiece to create a weld pool of moltenmaterial, and the weld connector is subsequently displaced into the weldpool, an airborne fluid residue of the weld pool is deflectable awayfrom the threads of the threaded weld connector by the fluid flow. 32.The apparatus as claimed in claim 31, comprising means for inducing saidfluid flow at least substantially simultaneously with the creation ofthe weld arc.